1. Field of the Invention
The subject invention relates to a system for detecting and removing undesirable noise from radio signals, such as beats and tones.
2. Discussion
Radio receivers and especially in vehicle mounted radio receivers are susceptible to interference noise, from a variety of sources, including electronic devices. These interference noises may be mixed into a signal received by a receiver and thereby detract from the quality of the receiver's audio output. Some of such mixed in interference noises are commonly known in the industry as beats or tones. A beat or tone is more specifically a received interference that is generally a sinusoid of large enough amplitude to interfere with the reception of the desired received signal.
Beats generally occur when two sound waves of different frequencies having alternating constructive and destructive interferences cause the sound output to be alternatively soft and loud, the frequency of which is known as a beat frequency. The beat frequency is generally equal to the absolute value of the difference in frequency of the two waves.
Tones are noise frequencies outside the desired band broadcast. When two or more tones are present outside a particular frequency, the product resulting from the mixing of these tones could manifest as a distortion, an undesirable audio tone, or even in some circumstances could overpower the desired broadcast and substantially quiet the receiver.
Traditionally, to overcome beats or tones, once a particular interference was detected, either the receiver or the interfering component, if ever found, was redesigned to eliminate the beat or tone. While redesigning a receiver to minimize internal interferences, it is much more difficult to design a receiver to minimize outside interferences. The problem with beats and tones is particularly acute when a receiver is placed in a vehicle due to the confined space being packed with a multitude of components that may cause interference. As vehicle manufactures have added numerous electronic devices, controllers, communication tools and entertainment devices, the interference of beats and tones with audio signals has increased.
Many times beats or tones first manifest in prototype versions of a vehicle making them very expensive to eliminate. To eliminate or reduce beats and tones, the component or in some circumstances the components must be found. If the component causing the interference is found, it needs to be redesigned or eliminated, typically an impractical and expensive solution given the stage of vehicle development where these interferences are typically discovered. Even if all beats or tones are found and eliminated or reduced to an acceptable level, interferences may still occur from consumer devices introduced to the vehicle environment by the user, such as, a cell phone.
As such, it is desirable to have an improved system for detecting and removing beats and noise from radio signals that is less time consuming and more cost efficient than redesigning either components or the receiver, and can address and reduce or eliminate beats or tones caused by the consumer devices.